What makes the web application perform and scale better is always a big topic. And finding the performance problems and tuning them is another...

Here is some my thoughts of how to "finding" performance problems:

For a "new" api/application or other

• Analzying the detail api and then preparing the Jmeter/Grinder testing scripts for it.
• Using different load to identify the threshold for the api
• Adding profiling codes find the slownes
• Restart from point one again..

For a "old" api/application or other

• Analyzing the user pattern from the access detail log
• Simulate the real user load to find the slowness
• Adding profiling codes find the slownes
• Restart from point one again..

So,how can you identify the performance problems?